PVA-KH792-Enhanced Composite Cementitious Material from Lead–Zinc Slag and Electroplating Sludge: Mechanical Performance and Heavy-Metal Immobilization

To address the limited simultaneous optimization of mechanical performance and heavy-metal stabilization in waste-based alkali-activated systems, this study investigates the development and characterization of a novel composite cementitious material for potential construction applications, utilizing lead and zinc smelting slag (LZSS) and electroplating sludge (ES) as precursors. The novelty of this study lies in the co-modification of an LZSS-based alkali-activated matrix with PVA and KH792 to improve both compressive behavior and heavy-metal stabilization in ES-containing specimens. Based on single-factor optimization, the optimal matrix was obtained at 3.5% alkali content, a water-glass modulus of 1.4, and a liquid-to-solid ratio of 0.22, followed by 28 days of curing before testing. On this basis, ES and PVA-KH792 were introduced to investigate their effects on mechanical behavior, heavy-metal leaching, and immobilization mechanisms. The results showed that adding ES reduced the compressive strength of the alkali-activated matrix, whereas PVA-KH792 modification partially restored matrix integrity and improved performance. At 5% ES content, the compressive strength of the modified specimen increased by 7.66% compared with that of the unmodified ES-containing sample. More importantly, under the sulfuric acid–nitric acid leaching method, the Cr leaching concentration decreased from 20.1 mg/L to 13.7 mg/L, meeting the relevant regulatory limit (GB5085.3-2007 and EPA limit). Microstructural and spectroscopic analyses indicated that the beneficial effect of PVA-KH792 was associated with matrix densification and enhanced heavy-metal immobilization. The immobilization mechanisms were mainly attributed to Cr(VI) reduction by Fe(II), complexation/coordination with functional groups introduced by PVA-KH792, and physical encapsulation within the alkali-activated matrix. The findings provide a promising approach to waste valorization and the development of sustainable building materials, contributing to resource efficiency and reducing the environmental impact of the construction sector.